The detection of liquid or fluid level is one of many functions for which fiber-optic sensors are more suitable than their electrical counterparts, especially in noisy or hostile environments. Current sensors are typically arranged as simple on-off level switches which sense a sudden increase in optical radiation loss from an uncladded optical fiber making contact with a material liquid or fluid. An array of such "point" sensors may be used to detect a number of discrete levels; however, such a system is complex and provides discontinuous indication of level.
U.S. Pat. No. 5,072,617 shows a sensor configuration where a diaphragm is deflected by pressure of a liquid. Light is reflected off of one face of the diaphragm, and the reflected light is transmitted through several additional fibers. This is a relatively complicated arrangement.
Various other sensors are known in the art for measuring liquid level, but their use may be limited if: 1) they require fibers or other optical components to be immersed in the liquid, which immersion could modify the optical characteristics of the fiber as a result of "wetting" or corrosion; 2) they require light to pass through a liquid whose refractive or absorptive properties effect the operation of the sensor, thereby limiting their operation with certain liquids, especially opaque ones; or 3) they are complex and rely on components which are not common in the fiber-optics industry. What is needed is a level sensor which is simple, uses available components, and is relatively economical for commercial use.